1. Field of the Invention
The present invention relates to a control device and control method of a compressor.
2. Description of the Related Art
A process compressor (hereinafter called a “compressor”) is widely used for providing compressed gas in various types of plants such as plants in petrochemistry field. A compressor must be appropriately controlled to provide a stable discharge pressure or discharge flow rate required for a downstream process. However, when the flow rate becomes lower than a certain threshold, an unstable phenomenon called “surge” occurs in the compressor. Here, the surge means a vibration phenomenon that is accompanied by a pressure fluctuation or a backward flow in the compressor.
In general, an anti-surge valve is used for prevention of a surge or a breakaway from a surge in a compressor. By opening the anti-surge valve to return gas from the discharge side to the suction side, it is possible to stabilize the behavior of the compressor. In other words, the anti-surge valve is used to prevent the operating point of the compressor from entering a surge region or to shift over from the surge region to the operative region. As a control method of an anti-surge valve of a compressor, PID control is generally used to keep or shift the operating point on the operative region side from the surge control line on an HQ map. Meanwhile, the surge region and surge control line in a compressor will be explained later.
In Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. JP1999-506184, there is described a control system including: a PID control module that responds to a control variable (which corresponds to an “operating point” in the present invention), and a velocity control module that responds to a velocity signal which shows a velocity to a surge control line. In addition, JP1999-506184 describes that the control system is provided with an output signal selector for selectively outputting the first output signal outputted by the PID control module and the second output signal outputted by the velocity control module to an anti-surge valve.
In Japanese Unexamined Patent Application Publication No. JP2009-47059, there is described an operational method of a motor-driven compressor which controls the opening degree of an inlet guide vane of the compressor, and shifts the operating point of the compressor along a control line for start-up.
Here, the control line for start-up is set parallel to the surge line in the performance curve of the compressor and in the operative region side relative to the surge control line.
The control system of the compressor of JP1999-506184 is described with a case in which the compressor is operated on the premise that the compressor system has been designed under optimal conditions. However, the operational status of the compressor changes in accordance with the conditions of gas treated by the compressor and seasonal changes. In other words, when the control system described in JP1999-506184 is applied to an actual compressor system, the operator of the compressor is required to adjust PID parameters for anti-surge control by the try-and-error method.
Similarly, the operational method of a motor-driven compressor described in JP2009-47059 is based on the premise that the compressor system has been designed under optimal conditions. Accordingly, also in the invention described in JP2009-47059, the operator of the compressor is required to adjust PID parameters for anti-surge control by the try-and-error method.
Here, adjusting PID parameters for anti-surge control plays a key role in the start-up process of the compressor.
Accordingly, the present invention addresses providing a control device and control method of a compressor, which are capable of saving efforts of adjustment.